Ships and other nautical vessels are frequently under way at night. Generally, unaided human sight is relied on for steering and navigating the vessel at night. Lights on other ships and on shore often provide enough information to a ship's captain or helmsman to avoid major obstacles, especially when in the open sea. However, along the intracoastal waterway, and in lakes and rivers and ocean shores there are often many unmarked obstacles that are dangerous and must be avoided.
Radar is often used to aid human sight in spotting and tracking other vessels on the open sea and large harbors, especially at distances greater than can be seen with the naked eye. However, in confined areas, the radar image reflected by the surrounding terrain and other objects on or near the water will typically be somewhat cluttered and often will not clearly delineate the shore or other obstacles and hazards due to differences in reflectivity of the various objects.
More recently, devices used by the military for amplifying or intensifying ambient light have become commercially available and have been proven useful for navigating marine vessels in low light and nighttime conditions in confined areas. These light intensification devices are hand-held, requiring a captain or other individual responsible for steering the ship or vessel to periodically stand in a location best for viewing.